Printing method and printing apparatus

ABSTRACT

Regarding filling of a paste, a temperature gradient at a paste-pressing face is managed by a heater incorporated in a filling head. Alternatively, a nonvolatile component is applied to a printing face of a base material before the paste is filled, thereby preventing a volatile component of the paste from evaporating with time. Viscosity of the paste is thus maintained. Meanwhile, a change of the quantity of the paste is coped with by changing a moving speed of the filling head or a contact angle of the filling head to the printing face, or by supporting the filling head at the side in touch with the printing face.

TECHNICAL FIELD

This is a continuation application of U.S. patent application Ser. No.08/983,448, now U.S. Pat. No. 6,135,024, filed on Mar. 25, 1998 whichwas the national phase application of international applicationPCT/JP96/01929, filed Jul. 12, 1995.

The present invention relates to a printing method and a printingapparatus for filling a printing material into openings of a printingface of a body to be printed, and more particularly, to a printingmethod and a printing apparatus for applying paste, and to an apparatusfor manufacturing circuit boards for electronic devices, etc.

BACKGROUND ART

Recently, circuit boards have been changed from single-face boardshaving circuits formed on one face, to double-face boards and multilayercircuit boards so as to achieve compact and high-performanceapparatuses. Many of the boards adopted at present are advancedmultilayered ones. In the meantime, a printing technique using a fillinghead, i.e., a squeegee is employed in order to press and fill a pasteinto openings such as via holes or through holes in these circuitboards, or to press and fill the paste into openings of a metal mask toform circuits on the board. A lot of conditions are involved in theprinting technique, for instance, hardness of the squeegee, angle of thesqueegee to a printing face, pressure of the squeegee to the printingface, filling speed of the squeegee to the openings of the printingface, etc. Even a slight error in setting of the conditions adverselyinfluences the quality of printing films, and therefore the setconditions are adjusted based on experiences on the production line,thereby improving yields in the paste filling process and quality ofproducts.

Some adaptations are also made to the aforementioned squeegee in thefilling process. For example, the squeegee is improved in shape to havea flat, a sharp, or a curved contact face as the printing face. In onearrangement, a heater is built in the squeegee to heat the squeegeeitself to a fixed temperature, thereby lowering a viscosity of the pasteand increasing filling efficiency for the paste to the openings of theprinting face.

The viscosity of the paste increases in proportion to an operating timeof the squeegee. For stabilizing the viscosity, therefore, the paste isexchanged at a fixed time interval, or an organic solvent is added tothe paste to adjust the viscosity.

Meanwhile, the amount of the paste filled into the openings, e.g., viaholes and through holes, etc. or the openings of the metal mask iscontrolled and stabilized by filling the paste up to a surface of theopenings.

An example of the conventional circuit board-manufacturing method willbe described with reference to FIGS. 13A, 13B.

FIGS. 13A, 13B respectively represent examples of a manufacturing methodand a manufacturing apparatus for circuit boards in the filling processaccording to the conventional art.

In FIGS. 13A, 13B, 300 denotes a metal mask placed on a base material301. 303 and 305 denote squeegees which move on the metal mask 300 whilekeeping touch with the metal mask 300. 304 denotes a paste, and 302denotes a stage. The base material 301 is disposed in touch with on thestage 302. The metal mask 300 is arranged with a slight space above thebase material 301, onto which the paste 304 is supplied. The squeegees303, 305 located above the metal mask 300 can move in an up/downdirection and in a printing direction of the squeegees 303, 305.

The paste is filled in the thus-constructed apparatus in a processdescribed herein. The base material 301 is first set at a predeterminedposition on the stage 302. A through hole 301 a formed in the basematerial 301 is registered with a hole 300 a formed in the metal mask300, and the metal mask 300 is set above the base material 301. Thepaste 304 is supplied onto the metal mask 300. The squeegees 303, 305are lowered to hold the base material 301 by pressing a predeterminedpressure on to the material 301. Thereafter, the squeegees 303, 305 aremoved in the printing direction to move the paste 304 on the metal mask300, thereby printing onto the base material 301. The paste 304 ispressed and filled in the through holes 301 a formed in the basematerial 301 in this manner.

In the above paste filling process in the conventional art, a fillingshape or the filling amount of the paste 304 is greatly changed even bymechanical errors, resulting in blanking, insufficient printing, orsimilar filling failures. When the flat squeegee 305 shown in FIG. 13Bis used, a contact angle of the squeegee to the printing face of themetal mask 300 or base material 301 is hard to fix and maintain. Theamount of the paste filled in the through hole 301 a varies greatly andis considerably difficult to control properly. This is an importantissue. In the case of the square squeegee 303 as shown in FIG. 13A, thecontact angle of the squeegee to the printing face of the metal mask 300or base material 301 is easy to set. A front end part of the squaresqueegee 303 in touch with the printing face of the base material 301 isnot sufficiently sharp, and consequently the paste 304 is left on themetal mask 300 or base material 301. The front end part of the squaresqueegee can hold only a small amount of the paste 304. This makes itnecessary to frequently replenish the paste 304, and thus deterioratesproductivity. When a viscosity of the paste 304 is increased because ofthe evaporation of volatile components or when the paste of a highviscosity is used, considerably less paste is filled than if kept underthe originally properly set conditions. In other words, the fillingcondition should be re-set during operation although this takes a longtime. This is another issue. In the case where a heater is incorporatedin the squeegee 303, 305, this arrangement merely lowers the viscosityof the paste 304. This does not effectively influence the rolling orfilling of the paste 304 and raises the necessity for setting andadjusting the conditions again. Poor productivity still remains as anissue.

The object of the present invention is therefore to provide a printingmethod and a printing apparatus whereby a sufficient filling amount of aprinting material into openings of a body to be printed is secured inconformity with various filling conditions, to thereby improve yields,quality, and productivity for printing with the printing material.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda printing method for pressing and filling a printing material by meansof a filling head to openings of a body to be printed, wherein a flowpressure of the printing material is kept roughly constant duringprinting of the printing material.

According to a second aspect of the present invention, at least either acontact angle of the filling head to a printing face of the body to beprinted or the speed of the filling head can be changed in accordancewith a change of the amount of the printing material in the above firstaspect, thereby keeping the flow pressure of the printing materialroughly constant.

According to a third aspect of the present invention, printing of theprinting material can be conducted in the above first or second aspectwhile the filling head is supported at the side (first side) of apressing face thereof in touch with the printing face of the body to beprinted, thereby keeping the flow pressure of the printing materialroughly constant.

According to a fourth aspect of the present invention, in any one of theabove-described first-third aspects of the invention, a temperaturegradient can be applied to the pressing face of the filling head so thata temperature of a part in touch with the printing face of the body tobe printed is higher than that of a part away (second side) from theprinting face of the body to be printed and the filling head, therebykeeping the flow pressure of the printing material roughly constant.

According to a fifth aspect of the present invention, in any one of thefirst through fourth aspects, a pretreatment material can be appliedbefore the printing material is filled by the filling head into theopenings at the printing face of the body to be printed, thereby keepingthe flow pressure of the printing material roughly constant.

According to a sixth aspect of the present invention, there is provideda printing apparatus for pressing and filling a printing material by afilling head into openings of a body to be printed, which includes aholding device for keeping a flow pressure of the printing materialroughly constant during printing of the printing material.

According to a seventh aspect of the present invention, the holdingdevice in the sixth aspect can be a control part which changes at leasteither a contact angle of the filling head to a printing face of thebody to be printed, or the speed of the filling head in accordance witha change of the amount of the printing material.

According to an eighth aspect of the present invention, the holdingdevice in the seventh aspect can be a supporting member for supportingthe filling head at the side of a pressing face thereof in touch withthe printing face of the body to be printed.

According to a ninth aspect of the present invention, the holding devicein any one of the sixth through eighth aspects can have atemperature-adjusting element which applies a temperature gradient tothe pressing face of the filling head so that a temperature of a part intouch with the printing face of the body to be printed is higher thanthat of a part away from the printing face of the body to be printed andthe filling head.

According to a tenth aspect of the present invention, thetemperature-adjusting element in the ninth aspect can be adapted to setan optimal temperature gradient along the pressing face of the fillinghead from the side in touch with the printing face of the body to beprinted.

According to an eleventh aspect of the present invention, the holdingdevice in any one of the sixth through tenth aspects can have apretreatment head for applying a pretreatment material to the fillinghead and the printing face of the body to be printed before the printingmaterial is filled.

According to the present invention, during filling of the printingmaterial, the flow pressure of the printing material is kept roughlyconstant, so that a sufficient filling amount of the printing materialis secured into openings of the body to be printed in conformity withvarious filling conditions, thereby improving a yield, quality, andproductivity of printing.

In the printing method and the printing apparatus of the above describedaspects of the present invention, the filling head moves to press andfill. the printing material into openings of the base material or metalmask. At least either the contact angle of the filling head in relationto the printing face of the base material or metal mask, or the speed ofthe filling head is changed under a predetermined condition. Forinstance, a predetermined condition could be changing amount of theprinting material as the filling head moves forward. Therefore, the flowpressure of the printing material is kept roughly constant to cope withan increase of a viscosity of the printing material with time or adecrease of the filling/pressing force due to the consumption of theprinting material, etc. A predetermined amount of the printing materialis stably secured at all times, thereby improving continuous printingefficiency.

According to the printing method and the printing apparatus of thefurther aspects of the present invention, the filling head is supportedat the side of the pressing face thereof in touch with the printing faceof the base material or metal mask. The side away from the printing faceis rendered a free end and deformable, so that required flexibility isattained. The printing material is controlled so as to not leak whenpressed by the filling head at the side in touch with the printing face.A necessary minimum elasticity is ensured for the filling head to tracethe uneven printing face of the base material or metal mask. The flowpressure of the printing material is thus maintained roughly constant. Apredetermined amount of the printing material is stably filled withoutany special control means against an increase of the viscosity of theprinting material with time and reduction in volume of the printingmaterial because of the consumption. Continuous printing efficiency canbe improved.

In the printing method and the printing apparatus of the yet furtheraspect of the present invention, a predetermined temperature gradient isapplied to the pressing face of the filling head. The temperature at theside of the pressing face in touch with the printing face is made highand the temperature decreases along the pressing face away from theprinting face. As a result, the viscosity of the rolling printingmaterial in touch with the printing face is lowered, thereby improvingfluidity of the printing material and maintaining the nearly constantflow pressure of the printing material. At the same time, thetemperature at the side of the pressing face away from the printing faceis lower, whereby the fluidity is limited. Thereby hydraulic pressure ofthe pressing face of the part in touch with the printing face increases.Accordingly, not only a predetermined amount of the printing material isstably filled, but the evaporation of volatile components is restrictedat the low temperature part. All of the printing material can be easilymaintained at a predetermined viscosity, and continuous printingefficiency can be improved.

With the use of the temperature-adjusting element for applying theabove-described temperature gradient, and when the temperature-adjustingelement is constituted to set an optimal temperature gradient to asection of the pressing face away from the printing face of the basematerial or metal mask, circuit boards of various conditions can bemanufactured with high quality in accordance with a variety of printingmaterials and filling conditions.

In the printing method and the printing apparatus of the differentaspects of the present invention, in addition to the pressing andfilling of the printing material by means of the filling head toopenings of the base material or metal mask, the pretreatment head thatis additionally provided is driven to apply the pretreatment material tothe printing face of the base material or metal mask prior to thefilling of the printing material. The effect of applying the nonvolatileorganic substance can be achieved in one single filling process. If thepretreatment material, e.g., nonvolatile organic component. contained inthe printing material is applied onto the body to be printed before theprinting material is filled, an increase of the viscosity of theprinting material can be suppressed. Thereby the flow pressure of theprinting material. is maintained nearly constant and the continuousprinting performance improves. Although the volatile componentevaporates after the printing, the nonvolatile component adsorbs intothe printing face which results in a change of a composition of theprinting material. As such, the nonvolatile component is appliedbeforehand to prevent the change of the composition.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe preferred embodiments thereof- with reference to the accompanyingdrawings, in which:

FIG. 1 is a diagram of a part with a paste-filling function for acircuit board-manufacturing apparatus in which a printing apparatus forexecuting a printing method in a first embodiment of the presentinvention is installed;

FIG. 2 is a block diagram of a control circuit related to thepaste-filling part of the apparatus in FIG. 1;

FIG. 3 is a diagram of a part with a paste-filling function of a circuitboard-manufacturing apparatus in which- a printing apparatus forexecuting a printing method in a second embodiment of the presentinvention is installed;

FIG. 4 is a block diagram of a control circuit related to thepaste-filling part of the apparatus of FIG. 3;

FIG. 5 is a diagram of a part with a paste-filling function of a circuitboard-manufacturing apparatus in which a printing apparatus forexecuting a printing method in a third embodiment of the presentinvention is installed;

FIG. 6 is a diagram of a part with a paste-filling function of a circuitboard-manufacturing apparatus in which a printing apparatus forexecuting a printing method in a fourth embodiment of the presentinvention is installed;

FIG. 7 is a diagram explanatory of an arrangement of a low temperatureheater of a filling head in FIG. 6;

FIG. 8 is a diagram of a temperature distribution of a face of thefilling head of FIG. 6 in touch with a paste;

FIG. 9 is a diagram of a part with a paste-filling function of a circuitboard-manufacturing apparatus in which a printing apparatus forexecuting a printing method in a fifth embodiment of the presentinvention is installed;

FIG. 10 is a diagram of a part with an applying function for anonvolatile organic component in a paste of a circuitboard-manufacturing apparatus in which a printing apparatus forexecuting a printing method in a sixth embodiment of the presentinvention is installed;

FIG. 11 is a graph of results of a viscosity increase when thenonvolatile organic component in the paste is applied onto a basematerial and when the nonvolatile organic component in the paste is notapplied onto the base material in the sixth embodiment;

FIG. 12 is a diagram showing a state of the paste after filled accordingto a circuit board-manufacturing method representing a seventhembodiment of the present invention; and

FIGS. 13A, 13B are diagrams of conventional printing apparatuses.

BEST MODE FOR CARRYING OUT THE INVENTION

Before the description of the present invention proceeds, it is notedthat like parts are designated by like reference numerals throughout theaccompanying drawings.

In order to describe a printing method and a printing apparatus inembodiments of the present invention, a method and an printing methodand printing apparatus provided will be depicted below with reference tothe drawings.

First Embodiment

FIGS. 1, 2 are diagrams of an apparatus used in a filling process inorder to manufacture circuit boards with a printing method and aprinting apparatus according to a first embodiment of the presentinvention provided.

As is schematically illustrated in FIG. 1, in the apparatus used in thefilling process, a filling head 21 for filling a paste 22 (an example ofthe printing material) onto a base material 4 (an example of the body tobe printed) on a stage 5. The filling head 21 is moved. in a fillingdirection, e.g., by a pair of right and left transverse guides 25parallel in the drawing to a printing face of the stage 5 and atransverse slider 26 guided by the guides. The filling head 21 is alsomoved up and down by a pair of vertical guides 27 arranged above theslider 26 in a vertical direction and a slider 28 guided by the guides27. The filling head 21 is pivotally supported by a shaft 29 on thevertical slider 28 in a rotatable fashion. At this time, a part of thefilling head 21 in touch with the base material 4 is a free end. Acontact angle θ between the filling head 21 to a printing face of thebase material 4 is variable.

The filling head 21 is rotated about the shaft 29 by driving of anactuator A1 coupled to the shaft 29 and set on the vertical slider 28.Moreover, the filling head 21 is moved up and down via the verticalslider 28 by driving of an actuator A2 coupled to the vertical slider 28and mounted to the transverse slider 26. The filling head 21 is alsomoved right and left via the transverse slider 26 by driving an actuatorA3 coupled to the transverse slider 26. Each actuator is constructed by,for example, a motor, a ball screw shaft coupled to a rotary shaft ofthe motor and a nut screwed to the ball screw shaft and fixed to adriven member.

FIG. 2 shows an example of a control circuit for controlling driving ofthe actuators A1, A2, and A3 in the first embodiment. Each of theactuators A1-A3 is controlled by a control part 31 which is amicrocomputer through drivers 201, 202 and 203 respectively. Variouscontrol conditions including changing speed (printing speed) conditionsfor the filling head 21 are inputed through an operation panel 32.

Information from sensors detecting an angle, speed, and height of thefilling head 21 in relation to the printing face of the base material isinputed into the control part 31. Based on the information detected, thecontrol part 31 of the control circuit through drivers 201, 202, and 203feedback-controls the actuators A1, A2, and A3 so that information fromsensors detecting the angle, speed, and height of the filling head 21 inrelation to the printing face of the base material conforms to setvalues.

In the conventional printing method, a set angle of a squeegee to theprinting face of the base material is kept constant during filling ofthe paste irrespective of the feeding amount of the paste. However, ahydraulic pressure generated in the paste 22 decreases as the amount ofthe paste 22 is reduced, while lowering a filling force. D.E. Riemarreports the following correlation in “INK HYDRODYNAMICS OF SCREENPRINTING”, Proceedings of the 1985 ISHM Symposium, pages 52-58.

p=kμv{square root over (V)}/sin² θ  (1)

In the equation (1), p is a pressure generated in the paste 22, μ is aflow velocity of the paste 22, v is a speed of the filling head 21, V isa volume of the paste 22, θ is a contact angle of the filling head 21 inrelation to the printing face of the base material 5, and k is aproportional constant.

A pressure difference expressed by the equation (1) is the pressuredifference necessary for filling the paste 22 into a through a hole 4 d.Hole 4 d is an example of an opening formed in the base material 4. Apaste filling state for hole 4 d is detected by substituting thepressure difference to the technologically well known Hagen-Poiseulle'slaw. Therefore, in order to make the filled state of the paste 22constant, it is important to always maintain the pressure p generated inthe paste 22 at a constant pressure during printing.

Conventionally, enough paste is generally supplied to ignore thedecreasing amount of paste volume for an even continuous paste-fillingoperation. However, this does not solve a viscosity change or acomposition change of the paste itself.

On the other hand, according to the method of the first embodiment, thereducing amount of the paste 22 in one printing operation, namely, inone stroke of the filling head 21 is done beforehand. The speed of thefilling head 21 is increased from v to a speed obtained by an expression(2) shown below, thereby coping with the volumetric change of the paste.The feeding amount of the paste 22 for each time can thus be reduced.$\begin{matrix}{v\left( {{\sqrt{V}/\sqrt{\left( {V - {\Delta \quad V}} \right)}} - 1} \right)} & (2)\end{matrix}$

The expression (2) is obtained by solving the foregoing equation (1) andthe following equation (3). $\begin{matrix}{p = {k\quad \mu \quad v{\sqrt{V - {\Delta \quad V}}/{\sin^{2}\left( {\theta - {\Delta \quad \theta}} \right)}}}} & (3)\end{matrix}$

wherein ΔV>0.

Since the speed of the filling head 21 is changed in accordance with thechanging amount of paste 22, the pressure generated in the paste 22 ismaintained constant, and consequently the amount of the paste 21 filledin the through hole 4 d of the base material 4 becomes constant.

Changes of the filling force for the paste after 100 sheets are printedin the conventional method based on an initial feed amount of the pasteand the method of the first embodiment (new technique) are confirmed inTable 1 in terms of a changing ratio of a filling depth of the paste.Regarding the above description of “based on the initial feed amount ofthe paste”, this implies that the paste is not added after onceinitially supplied. The initial amount is compared with the amount ofpaste after 100 sheets are printed, and the result is represented by thefilling rate in Table 1. For instance, when the amount of paste is 500g, a difference from a filling rate 100-99.5% is the changing ratio ofthe conventional method. In the method of the first embodiment, theamount of the paste is not changed and therefore the filling rate is100% and the changing ratio before and after printing is 0%.

TABLE 1 Filling rate up to Filling rate up filling depth in to fillingdepth Amount of paste conventional method in new technique 500 g 99.5%100% 300 g 99.2% 100% 100 g 97.5% 100%  50 g 94.9% 100%  30 g 91.3% 100%

As is clearly confirmed from Table 1, the speed control to the fillinghead 21 in the first embodiment is effective.

As described herein and above, since the moving speed of the fillinghead 21 is controlled by the control part 31 via the actuator A3 inaccordance with the change of the amount of the paste 22 duringprinting, the pressure generated in the paste 22 is maintained constant,whereby the filling amount of the paste 22 into the through hole 4 d ofthe base material 4 is uniform. The paste can be continuously printedefficiently, with productivity improved.

In the above-described first embodiment, the speed of the filling head21 is controlled to maintain constant the pressure in the paste 22. Onthe other hand, the angle of the filling head 21 to the printing face ofthe base material can be controlled by driving the actuator A1 inaccordance with the changing amount of the paste 22, thereby holding thepressure in the paste 22 constant. The same effect can be achieved inthis manner as well. More specifically, Δθ satisfying the followingequation (4) is obtained and the actuator A1 is driven by the controlpart 31 so that the angle of the filling head 21 is reduced every Δθ,whereby the same effect as achieved by the above speed control can berealized. $\begin{matrix}{{\sin \left( {\theta - {\Delta \quad \theta}} \right)} = {\sqrt{\left. {\sqrt{\left( {V - {\Delta \quad V}} \right)}/\sqrt{V}} \right)}\sin \quad \theta}} & (4)\end{matrix}$

The contact angle θ to the printing face of the base material 4 isautomatically changed in the first embodiment by rotating the fillinghead 21 about the shaft 29 by the actuator A1. The filling rate is alsoimproved by reducing the contact angle θ, thereby coping with thechanging amount of paste. Needless to say, when the contact angle θ ofthe filling head 21, specifically, free end of the filling head in touchwith the printing face is changed, a height of the free end is changed,which should be corrected by suitably driving the actuators A2 and A3 bythe control part 31 to suitably move the filling head 21 up/down andright/left to maintain the filling head 21 at a predetermined height.This way of angle correction to a predetermined angle is unnecessary ifthe filling head shown in FIG. 5 is used.

In the first embodiment, both the speed and the contact angle θ of thefilling head 21 may be adapted to meet the changing amount of paste.

Second Embodiment

FIGS. 3, 4 are diagrams of an apparatus used in a paste-filling processin the manufacturing of circuit boards in which there is provided aprinting method and a printing apparatus according to a secondembodiment of the present invention. The apparatus fundamentallyoperates the same effect as in the first embodiment. What is differentfrom FIGS. 1, 2 is that the contact angle θ is changed to apredetermined value by the actuators A2, A3 while the driver 201 and theactuator A1 for driving the filling head 21 are eliminated. An anglesensor 100 is installed instead to detect an angle of the filling head21 on the shaft 29. The contact angle θ is changed due to deflection ofthe filling head 21 caused by the actuators A2, A3. It is so constructedthat angle information detected by the angle sensor 100 is inputed tothe control part 31. Control part 31 in turn controls the angle of thefilling head 21 to the predetermined value which is detected by theangle sensor 100, whereby the contact angle θ is kept at thepredetermined value.

Third Embodiment

As indicated in FIG. 5, in an apparatus used in a paste-filling processin a manufacturing apparatus for circuit boards in which there areprovided a printing method and a printing apparatus according to a thirdembodiment of the present invention, a filling head 121 has a squeegeeof a triangular prism laid laterally. Two sides of the filling head 121defining a right angle of a right triangle in lateral cross section areset schematically in parallel to the lateral direction and verticaldirection. A holder 41 for supporting the filling head 121 is fixed tothe filling head 121 along a vertical side. As shown in FIG. 5, theholder 41 supports a paste pressing face 121 a of the filling head 121in the vicinity of a part C which comes in touch with the printing faceof the base material 4 on the stage 5. A part D of the pressing face 121a separated from the printing face is rendered a free end. Morespecifically, although a flat squeegee is employable in the thirdembodiment, the squeegee actually used in the embodiment is a slightlymodified blade type of a triangular lateral cross section.

Thickness of the squeegee is gradually reduced from the part C of thepressing face 21 a in touch with the printing face to the part D apartfrom the printing face.

In a supporting structure for the conventional flat squeegee typefilling head, when the filling head 121 is lowered to touch the printingface of the base material 4 thereby impressing a printing pressure ontothe base material 4 in order to fill the paste 22 the pressure by theholder is applied in the vicinity of the part D. The part D of thepressing face 121 a is supported, whereas the part C in touch with theprinting face is free and easily deflected or broken. In other words,the paste 22 leaks and the pressure is less at the part C although thepressure is important to fill the paste 22 to the through hole 4 d ofthe base material 4. This results in failure in stable filling of thepaste 22.

Moreover, with the conventional filling head, the contact angle θdefined between the filling head and the printing face decreases from aninitially set value. Since the contact angle and the deflected contactpart of the filling head to the printing face varies depending on amaterial of the filling head and on a structure of a printing materialpressing part, adjustments are required.

When such a phenomenon occurs, the printing material filled in thethrough hole of the base material is undesirably scraped out. Thephenomenon will occur unless the deflected front end of the conventionalfilling head is restricted to a necessary minimum to let the fillinghead trace the uneven printing face of the base material.

Meanwhile, the conventional square squeegee initially has its fourcorners rounded and therefore scrapes the paste extraordinarily poorly.Although a required or larger amount of printing pressure is needed dueto the aforementioned poor scraping efficiency of the squeegee thescraping amount of the filled paste from the hole is unstable.

In contrast, according to the third embodiment of the present invention,the filling head 121 pressing and filling the paste 22 into the throughhole 4 d of the base material 4 is supported by the holder 41 at thepart C of the pressing face 121 a which is in touch with the printingface of the base material 4. Thus, the part D of the pressing face 121 aaway .from the printing face becomes free and deformable. Inconsequence, a required flexibility can be achieved for the filling head121 and the part C in touch with the printing face can suppress the lossof the pressing force in the paste 22. A required minimum elasticity fitto the uneven printing face of the base material 4 can be achieved byselecting an elastic material for the filling head 121. The filling head121 of the embodiment can thus stably fill a predetermined amount of thepaste 22 without a special control, even if the viscosity of the paste22 is increased with time or the amount of the paste 22 is reduced dueto the consumption. Continuous printing performance can be enhanced.

According to the third embodiment, the printing pressure acting on theprinting face from the holder 41 via the filling head 121 is directlyapplied to the part C in touch with the base material 4, so that thecontact angle can be less reduced even when the filling head 121 isdeflected. Practically no deflection is generated at the contact partbetween the filling head 121 and the base material 4, as is observed inexperiments. By employing the apparatus of the invention, conditions setfor the filling head 121 can be kept constant during printing of thepaste 22. If the printing apparatus is adapted for a circuitboard-manufacturing apparatus to print the paste onto the boards, itbecomes possible to maintain the set constant conditions for the fillinghead during manufacturing of the circuit boards, and produce circuitboards of constant quality. A manufacturing yield can be improved.

Fourth Embodiment

FIG. 6 is a schematic diagram of a process of filling a paste for acircuit board-manufacturing apparatus adopting a printing method and aprinting apparatus according to a fourth embodiment of the presentinvention.

As indicated in FIG. 6, a cylindrical filling head 221 is moved to pressand fill the paste 22 into the through hole 4 d of the base material 4held on the stage 5. At this time, the filling head 221 is not rotated.

The filling head 221 is made movable in an up/down direction and afilling direction shown by an arrow A in FIG. 6. In general, when thefilling head 221 moves on the base material 4, the paste 22 present inthe vicinity of a contact point between the filling head 221 and basematerial 4 is considerably hard to flow even if the viscosity of thepaste 22 is lowered, due to a small movable area where the paste 22 isallowed to move and a small pressure gradient in the neighborhood of thefilling head 221.

Although the fluidity of the paste 22 can be improved by raising atemperature of the paste 22, the life of the paste 22 is decreased ifthe paste 22 is a thermoset type. What is needed to secure the fluidityrequired for the paste 22 to be filled in the through hole 4 d of thebase material 4 is that only a part of the paste 22 which comes close tothe through hole 4 d of the base material 4 is heated. A force necessaryfor the paste 22 to be filled into the through hole 4 d is obtained byhydraulic pressure generated by the filling head 221 and by rolling ofthe paste 22 denoted by an arrow B (e.g., D. E. Riemer: “INKHYDRODYNAMICS OF SCREEN PRINTING”, Proceedings of the 1985 ISHMSymposium, pages 52-58).

The aforementioned rolling of the paste 22 is achieved when the paste 22moves up from the printing face of the base material 4 along a pastepressing face 221 a of the filling head 221. Therefore, if apredetermined temperature gradient is set on the pressing face 221 a ofthe filling head 221, the fluidity of the paste 22 can be improved. Morespecifically, the temperature gradient of the pressing face 221 a is setso that a temperature of the pressing face 221 a is high at the side intouch with the printing face of the base material 4, and the temperatureis lowered at the pressing face 221 a away from the printing face of thebase material 4. Thus, since the temperature of the pressing face 221 ais high at the side in touch with the printing face of the base material4, the viscosity of the rolling paste 22 is decreased. Therefore thefluidity of the paste 22 can be improved. On the other hand, since thetemperature of the pressing face 221 a is lowered at the side away fromthe printing face of the base material 4, the fluidity of the paste 22is restricted. The hydraulic pressure of the contact part between theprinting face of the base material 4 and the pressing face 221 a isincreased. Accordingly, a predetermined amount of the paste 22 is filledstably and at the same time, volatile components in the paste 22 areprevented from evaporating by the low-temperature part, making itpossible to easily maintain the whole paste 22 at a predeterminedviscosity. The paste 22 can show improved continuous printability.

Table 2 indicates a filling depth of the paste and a temperaturedifference in the filling head 221 under general filling conditions (forinstance, pressure of 2 kgf/cm², speed of 40 mm/sec, amount of the paste(feeding amount) of 500 g).

TABLE 2 Temperature difference (° C.) Filling depth (mm) 0 5 5 10 10 1215 13

As is understood from Table 2, the filling force is improved when thetemperature difference is not less than 5° C. (i.e., in the fourthembodiment wherein the temperature gradient is set for the pressingface) rather than when the temperature difference is 0° (i.e., in theconventional example using the filling head without the temperaturegradient). By way of example, the temperature difference is preferably10° C. when a solder paste is used.

According to the fourth embodiment, upper and lower heaters 24, 23 arebuilt in the filling head 221 so as to provide the pressing face 221 awith the temperature gradient as described above. In this arrangement,the lower heater 23 heats a part of the paste 22 in touch with theprinting face, and the upper heater 24 heats so that the paste 22separates from the printing face. The filling head 221 at the upperheater 24 has a lower temperature than the lower heater 23. As a result,the heaters 23, 24 realize such temperature gradient at the pressingface 221 a of the filling head 221 that the temperature of the pressingface 221 a at the side in touch with the printing face of the basematerial 4 is high, and decreases where the pressing face 221 a isfurther away from the printing face.

It is generally known that volatile components if contained in the pasteare lost subsequent to a temperature rise thereby increasing theviscosity of the paste. The part of the paste 22 away from the printingface and the filling head 221 exposed to the outside air is made lowerin temperature than the part at the pressing face 221 a in touch withthe printing face of the base material 4. Since this temperature is evenlower than an evaporation temperature of the volatile components, thepaste 22 can be prevented from being hardened as a result of theevaporation of the volatile components. The continuous printability canbe enhanced.

FIG. 7 is a diagram explanatory of an arrangement of the upper heater 24at the low-temperature side of the filling head 221. The upper heater 24is generally disposed, as is clearly shown in FIG. 7, to pass the centerof the filling head 221 in a low-temperature variable area 102approximately 30° above a plane 101 in parallel to the printing face ofthe base material 4. A position of the upper heater 24 should bedetermined within the above range from a relationship with the amount ofthe paste, because the paste 22 generally does not move up to thepressing face 221 a of the filling head 221 over the range. In casethere is supplied a large amount of the paste, the upper heater 24 ispreferably arranged slightly upward within the range. On the other hand,if the paste of a small amount is supplied, the upper heater 24 ispreferably installed slightly downward within the range. When the paste22 is a solder paste, it is preferred, e.g., that the lower heater 23heats the paste up to 45° C., while the upper heater 24 heatsapproximately to a room temperature. If the paste 22 does not includevolatile components, the paste may be heated up to 50° C. or 60° C. Whenthe paste 22 is maintained at approximately room temperature by theupper heater 24, the upper heater 24 may be set at a lower temperaturethan the room temperature to slightly cool the paste 22 heated by thelower heater 23. An apparatus shown in FIG. 9 which will be describedlater is preferably used if it is necessary to positively cool the paste22.

An example of the above-described temperature gradient is preferably acurve satisfying y=b−ax², as in FIG. 8, wherein b and a are constantsoptionally determined in accordance with characteristics of the paste22. In this graph, a position of the lower heater 23 in FIG. 6 isindicated as an origin of an axis of abscissa, and an intersection pointbetween the curve and the axis of abscissa is an arranging position ofthe upper heater 24.

The above temperature gradient may be similarly achieved by using onlythe lower heater 23 or interposing a suitable number of heaters betweenthe upper and lower heaters 24 and 23. The temperature gradient can bedefined more forcibly and finely if the number of heaters is large.Alternatively, a continuous single heater may be incorporated from thelower heater 23 to the upper heater 24 to gradually reduce thermalcapacity (generating calorie).

As is indicated in FIG. 6, in the fourth embodiment, variable resistors(volumes) 23 a, 24 a are set in an energizing circuit of the heaters 23,24, thereby regulating the amount of heat from the heaters 23, 24 toobtain the temperature gradient in various forms. Circuit boards ofvarious conditions can accordingly be manufactured with high degree ofquality to meet a wide variety of conditions for the paste 22 andfilling conditions for the paste 22.

Although the heaters 23, 24 are used as an example of thetemperature-adjusting element in the fourth embodiment, the element isnot limited to this and any optional element can be used so long as itcan adjust temperatures.

Fifth Embodiment

FIG. 9 is a schematic diagram of a process of filling a paste in acircuit-board manufacturing apparatus adopting a printing method and aprinting apparatus according to a fifth embodiment of the presentinvention. A difference from FIG. 8 is that the upper heater 24 iseliminated, and a cooling device 200 is set at a position correspondingto the position of the upper heater 24 to supply cool air onto thepressing face 221 a of the filling head 221. In the fifth embodiment,the lower heater 23 heats the part of the paste 22 in touch with theprinting face. The cooling device 200 prevents the part of the paste 22separated from the printing face and the filling head 221 from beingraised to a temperature not lower than a necessary temperature becauseof heating by the lower heater 23. Owing to this arrangement, a requiredtemperature difference is maintained between the part of the paste 22away from the printing face and the filling head 221 and the part of thepaste 22 in touch with the printing face.

Sixth Embodiment

FIG. 10 is a schematic diagram of a filling apparatus which shows apretreatment state before filling the paste to manufacture a circuitboard with a printing method and a printing apparatus according to asixth embodiment of the present invention provided.

In the sixth embodiment, as shown in FIG. 10, before the paste 22 ispressed and filled by the filling head 21 to the printing face of thebase material 4 on the stage 5, a pretreatment material 51, which is anonvolatile component included in the paste 22 is applied to theprinting face of the base material 4. The apparatus is equipped with thefilling head 21 and also a pretreatment head 52 for applying thepretreatment material 51. In a process of filling the paste 22, by thefilling head 21 to the through hole 4 d of the base material 4, the samenonvolatile organic component as contained in the paste 22 is applied asthe pretreatment material 51 by the pretreatment head 52 to the printingface of the base material 4 before the paste 22 is filled in the throughhole 4 d.

The pretreatment head 52 moves on the base material 4 while maintainingcontact with the base material 4 to apply the pretreatment material 51to the printing face of the base material 4. The pretreatment material51 is sufficiently scraped by the pretreatment head 52 from the printingface of the base material 4, but a part of the pretreatment material 51adsorbed by the printing face of the base material 4 is left on theprinting face of the base material 4. The adsorption on the printingface of the base material 4 during the filling of the paste 22 into thethrough hole 4 d causes an increase of the viscosity of the paste 22. Toresolve this viscosity increase of the paste 22, the same component thatadsorbs into the printing face of the base material 4 is preliminarilyapplied to the printing face of the base material 4 before the paste 22is printed. Since the component adsorbed into the base material 4 issupplied to the paste 22 during printing of the paste 22, the increaseof the viscosity of the paste 22 can be prevented.

Results of the viscosity increase of the paste 22 when the nonvolatileorganic component in the paste 22 is applied as the pretreatmentmaterial 51 onto the base material 4 beforehand (represented by“treated”) and when the pretreatment material 51 is not applied on thebase material 4 beforehand (represented as “not treated”) are shown inFIG. 11. As is apparent from FIG. 11, the viscosity of the paste isconstant when the nonvolatile organic component of the paste is applied,while the viscosity of the paste is increased when the organic componentis not applied. Therefore, the application of the nonvolatile organiccomponent can be effective to restrict the viscosity increase of thepaste.

From the graph of FIG. 11, the pretreatment material 51 is considered tobe scraped an equal amount to the paste 22 by the base material 4 andthe pretreatment head 52. If the scraping is not carried out enough, theorganic component remains on the surface of the base material 4 therebydecreasing the viscosity of the paste 22. Therefore, much care should betaken.

As the above result, the viscosity increase of the paste 22 isrestricted due to the application of the nonvolatile organic componentin the paste 22 onto the base material before the paste 22 is filled.The continuous printing efficiency. can be improved.

In the sixth embodiment, the filling head 21 and the pretreatment head52 are preferably formed in the same shape, structure, and material inorder to make the scraping condition equal. An application head for thepretreatment head 52 is a polyurethane squeegee in the above sixthembodiment, similar to the filling head 21. However, the same effect isobtained even when the organic component is adsorbed onto the basematerial by vapor deposition or the like manner.

Seventh Embodiment

FIG. 12 is an explanatory diagram of a state where the paste is filledin a paste-filling apparatus for circuit boards with a printing methodand a printing apparatus according to a seventh embodiment of thepresent invention provided.

According to the seventh embodiment, as shown in FIG. 12, a processpresses and fills the paste 22 into the through hole 4 d of thecompressive base material 4. When the paste 22 is filled into thethrough hole 4 d of the base material 4, 5-20% of the through hole 4 dis not filled with the paste 22, as designated by 61.

Accordingly, when the base material 4 is compressed, the paste 22 isallowed to escape into the non-filled part 61, thereby preventingdisconnection of connection parts in the layers of the circuit boardcaused by the expansion of the paste 22 if the non-filled part 61 didnot exist.

Concretely, after the paste 22 is filled in the through hole 4 d of thebase material 4, the base material is heated and pressed while heldbetween copper foils, whereby a double-face board is formed. Then, thecopper foils are etched in a predetermined pattern to thereby produce acircuit board. When the base material 4 is heated and pressed while heldbetween the copper foils in this series of operations, if the basematerial 4 is compressed by a degree larger than a tolerance for thepaste 22 filled in the through hole 4 d of the base material, the paste22 when hardened will generate a force which will separate the copperfoils from the base material 4. This brings about a large deteriorationin the connection reliability of the layers. This is caused due to apart of the paste 22 exceeding the tolerance cannot escape when thepaste filled in the through hole 4 d is compressed too much. The paste22 leaks into the base material 4 if the base material 4 is porous,resulting in a decrease of an insulation resistance, etc. and worseningreliability of the circuit board. This problem should be avoided.

When the non-filled part 61 is provided in the through hole 4 d of thebase material 4 to function as an expansion area for the paste 22, thecompressed paste 22 in excess of tolerance is accommodated within thethrough hole 4 d of the base material 4, so that the aforementionedissue can be eliminated. Table 3 shows good and defective connectionresistances when an average diameter of the through hole 4 d and depthof the non-filled part 61 in relation to the average diameter arechanged.

TABLE 3 Depth Depth of non- of non- Hole filled Hole filled Diameterpart Reliability Diameter part Reliability 200 μm  0% NG 100 μm  0% NG 5% OK  5% OK 10% OK 10% OK 20% OK 20% OK 25% NG 25% NG 150 μm  0% NG 5% OK 10% OK 20% OK 25% NG

From Table 3 above, when the non-filled part is 5-20% to the averagehole diameter is formed, the reliability of the connection resistancecan be ensured. From the above results, when the paste 22 is pressed andfilled so that the depth amount of the through hole 4 d of the basematerial 4 becomes 5-20% of the average diameter of the through hole 4 dof the base material 4, it can be shown that the connection parts of thelayers are separated by the repulsion force of the compressed basematerial 4. Thus, the reliability is deteriorated.

In each of the foregoing embodiments of the present invention, a directprinting method is described in which the filling head directly runs onthe printing face of the base material without using a mask. However,each embodiment is applicable in the same way where a mask (metal maskor the like) is set on the base material 4 and the filling head runs ona printing face of the mask.

As described in any of the first through seventh embodiments, the flowpressure of the paste is kept nearly constant while the paste (anexample of the printing material) is filled. The filling amount of thepaste is thus secured enough into the through hole(s) of the basematerial (an example of the body to be printed) in conformity withvarious filling conditions. The yield, quality, and productivity can beimproved in the present invention.

According to the printing method and the printing apparatus of theembodiment(s) of the present invention, at least either the contactangle of the filling head to the printing face of the base material ormetal mask, or the speed of the filling head is changed in accordancewith a predetermined condition, namely, a change of the amount of thepaste as the filling head moves forward. Even the increase of theviscosity of the paste or the decrease of the filling and pressing forcedue to the consumption of the paste with time can be handled in thismanner. A predetermined amount of the paste can be stably and surelyfilled thereby improving continuous printing performance.

In the printing method and printing apparatus of the embodiment(s) ofthe present invention, the filling head for pressing and filling thepaste into the through hole(s) of the base material or metal mask issupported at the side where the pressing face is in touch with theprinting face of the base material or metal mask. On the other hand, thefilling head at the side separated from the printing face is rendered afree end and deformable, thereby securing necessary flexibility. Whilethe pressure to the paste at the side in touch with the printing face isrestricted not to leak, a necessary minimum degree of elasticity isrequired to let the filling head trace the uneven printing face of thebase material or metal mask. A predetermined amount of the paste can bestably filled without any special control means provided against theincrease of the viscosity or reduction of the volume through consumptionof the paste with time. Continuous printing efficiency can be improved.

In the printing method and printing apparatus of the embodiment(s) ofthe present invention, the temperature-adjusting element is incorporatedwithin the filling head to apply the predetermined temperature gradientto the pressing face of the filling head. The temperature of thepressing face at the side in touch with the printing face is high andthe temperature is decreased as the pressing face is separated away fromthe printing face. The viscosity of the rolling paste of a part in touchwith the printing face is lowered thereby improving the fluidity of thepaste. At the same time, the fluidity at the pressing face at the sideaway from the printing face of the base material or metal mask and thefilling head is restricted because the temperature is lowered. Since thehydraulic pressure at the pressing face of the part in touch with theprinting face is increased, not only a predetermined amount of the pasteis stably filled, but the volatile component is prevented fromevaporating at the low temperature part. The whole paste can be easilymaintained at a predetermined viscosity and therefore continuousprinting efficiency can be improved.

When the heater (an example of the temperature adjusting element) is setto an optimal temperature gradient, high quality printing can beachieved in various conditions in conformity with a variety ofconditions of the paste and filling conditions of the paste.

In the printing method and printing apparatus of the embodiment(s) ofthe present invention, the pretreatment material is applied by thefilling head and the pretreatment head, provided side by side, beforethe paste is filled onto the printing face of the base material or metalmask. A positive effect of applying the nonvolatile organic substancecan be gained in one filling process. If the nonvolatile organiccomponent in the paste is applied onto the base material or metal maskbefore the paste is filled, the viscosity of the paste is prevented fromrising, therefore enhancing continuous printability.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims unless they departtherefrom.

We claim:
 1. A method of printing, which comprises: pressing and fillinga printing material into a through hole of a circuit board placed on astage and having a printing face with a filling head having a pressingface with a first side at which the pressing face contacts the printingface and a second side away from the first side; and maintaining aconstant flow pressure in the printing material in order to fill thethrough hole of the circuit board; wherein said maintaining comprisesholding said filling head such that said first side of said pressingface is held to be supported and said second side of said pressing faceis free and unsupported.
 2. A printing apparatus for pressing andfilling a printing material into a through hole of a circuit boardplaced on a stage and having a printing face, comprising: a filling headfor filling the printing material into the through hole, wherein saidfilling head has a pressing face which has a first side which contactsthe printing face during operation and a second side away from saidfirst side; and a holding device which supports said filling head atsaid first side so that a flow pressure of the printing material ismaintained constant, wherein said second side of said pressing face isfree and unsupported.
 3. A printing apparatus for pressing and filling aprinting material into a through hole of a circuit board having aprinting face, comprising: a filling head for filling the printingmaterial into the through hole, wherein said filling head has a pressingface which has a first side which contacts the printing face duringoperation and a second side away from said first side; and a holdingmeans for supporting said filling head at said first side so that a flowpressure of the printing material is maintained constant and so thatsaid second side of said filling head is free and unsupported.